It is known to use plastic containers in the food preparation and restaurant industry to package prepared foods. The typical food container of the prior art consists of a clear or solid colored base and a clear lid. In order to maintain the quality of food contents and prevent tampering with the contents of a sealed container, it is desirable that the food container, once initially sealed, not be capable of being initially opened without visible indication of the container having been opened. To achieve this feature, container manufacturers have designed containers having integral tamper evident features. Typically, these containers consist of a lid that is hingedly attached to a base. The lid seals to the base by superposing the rim of the lid upon the rim of the base. These types of plastic containers are sold as one-piece containers and are often referred to as “clamshell” containers or packages.
In one type of hinged tamper evident container, the lid and base each have interlocking elements respectively located on or near the lid rim and base rim where the two rims meet when the container is sealed (i.e., at a non-hinged side or portion of the container). The interlocking element of the lid or base is conventionally located on a tab or flange extending from the rim of the lid or base. Either or both of the tabs are attached to their respective rims by a frangible section of plastic. When the lid and base are placed in initial sealing arrangement, the interlocking elements on or near the lid rim and base rim engage and lock together. In order to open the initially sealed container, the frangible section of one or both tabs must be ruptured so as to release the tab or tabs from the container. Because the interlocking sealing elements are located on the tabs, rupturing one or more tabs from the container disables the locking mechanism. The ruptured tab provides evidence of the container having been opened. One shortcoming with the prior art food container described above is that the interlocked tabs can be cut from the container in clean fashion using scissors or another cutting implement so as to remove any indicia of the container having had a tamper evident mechanism. Also, with many tamper evident containers, one rim (typically the lid rim) superposes over the other rim (typically the base rim) such that at least one of the rim edges is exposed and subject to manipulation. With this type of sealing arrangement and construct in plastic containers, the lid and base can be partially pried open by inserting a thin object underneath an exposed rim edge at a point on the container distal from the tamper indicator. By partially prying open the rims in this fashion, one can doctor or tamper with the contents of the apparently sealed container without activating the tamper indicator.
In view of the issues presented by incorporating a tamper evident mechanism in the meeting rims of the hinged container, some manufacturers have incorporated tamper evident features as part of the structure that forms or includes the hinge. In these containers, the container is designed to require a severance near the hinge in order to unseal (initially open) the container. This construct make the hinge a single use hinge. These containers typically employ a square-shaped hinge arrangement (as seen from the side when the container is closed) in which the flange of the lid rim extends beyond the lid rim and then near-perpendicularly connects to a vertical segment that descends down from the lid flange. The vertical segment meets an extended portion of the base flange in similar near-perpendicular arrangement. The two flanges generally run parallel to each other and by their connection to the vertical segment form three sides of a square.
Square-shaped hinge containers suffer from a variety of deficits. One is a tendency of the container not to remain fully open for purposes of filling the container. The memory of the square hinge mechanism is such that the lid tends to rotate and cover all or part of the base. Another deficit is that the squeezing action required must move two adjacent, near perpendicular sides of the hinge structure and therefore the entire hinge structure must be effectively crushed in order to break the frangible line located at the bottom outside corner of the hinge structure. Thus, in order to rupture the frangible line, a squeezing force is applied to the entire box structure of the hinge area. This extended crushing motion may require the container to be stabilized with one's other hand in order to entirely rupture the frangible section.
Other tamper evident solutions involve using tabs that when activated remain attached to the container in a deformed condition and provide visible indication of the opening of the container. U.S. Published Patent Application No. 20100181323 (Thaler) is an example of one such tamper evident solution. This reference discloses a plastic food container that includes a lid adapted for sealing arrangement with a base. The rim of the base has an undercut formation adapted to receive the perimeter flange and flange tab of the lid when the lid and base are in the sealed arrangement. The flange tab includes an undercut release mechanism that allows a user to grasp a portion of the flange tab and initially open a sealed container via the extraction of the flange tab from the undercut formation by application of a pulling force to the undercut release mechanism. The flange tab includes tamper evident means that provides visible indication that the undercut release mechanism has been utilized to initially open the sealed container. A similar suggested tamper evident mechanism for food containers is that of U.S. 20100224630 (Petlak). With this tamper evident mechanism, a pull tab extends outwardly from at least one of the base or the cover. The surface of the pull tab has a series of grooves such that when the tab is partially separated from the lid or base via a pulling force, the tab is supposed to curl. This curling is intended to provide a visible deformation, which would be a signal to an end user that the container has been opened. With the containers of Thaler and Petlak, the lid rim inserts into the base rim to seal the container and therefore the pull tab must be extracted from within the confines of the base rim. This requires a complicated tab structure, as well as a tab and base rim mating arrangement.
In view of the features and deficits of the prior art containers, there is thus a need in the art for a re-closable plastic food container that is easy for end consumers to operate; combines reliable tamper evidence and defense against prying intrusion; and that uses a minimum of material to manufacture.